12 Bolt Diff service Questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Lippyp · 07-01-2003, 08:21 AM

I am going to pull the cover on my 12 bolt rear end and change the oil and give it a clean out. I have a new fel-pro gasket to go back on.

How much oil does an axle take, I have about 3 litres in the garage, will it need more than this? Should I use sealant with the gasket as well? ny idea on what the bolts should be torqued up to?

Which teeth do I count to work out my diff ratio and how do I work it out once I've counted?

Any other hints and tips that may help me would be welcomed.

Thanks

ginter · 07-01-2003, 08:55 AM

Not sure exactly how much it takes to fill a GM 12 bolt, but 3 litres (quarts, close enough) will be plenty. You probably already know that you just fill it up to the bottom of the fill hole right?

As for the gears, when you get the cover off, count the teeth on the ring gear. It's the biggest gear in there, you can't miss it. It runs the same rotation as the rear wheel and is the cause of the hump in the back of the diff cover. Then count the teeth on the pinion gear. It's the one that is directly connected (more or less) to the drive shaft where it comes into the diff. It's the second biggest gear in there, you can't miss it. Although it's buried in the back there a little bit (front of the differential actually, but you're looking at it from behind the truck so...). A scribe or paint mark near a tooth before you start counting will help here.

The gear ratio is just that. The ratio between the ring and pinion. On a 3.07 for example, the pinion gear will turn 3.07 times for every one turn of the ring gear.

HTH.

JimKshortstep4x4 · 07-01-2003, 09:17 AM

The differential will take approximately 3 1/2 pints, US measure.
I fill and check with my little finger. When I can touch the lube, it is full enough.

Usually the ring gear will be stamped with the number of teeth for the ring gear and the pinion, eg: 43:14 which is a 3:07.

Jim

smokekiki · 07-01-2003, 12:53 PM

Jim you must be right on the oil.My service manual said 4.5 pints.I got a little more than 3.5 before it started to run out the hole.

07-01-2003, 08:21 AM	#1
Lippyp English Chevy Owner Join Date: May 2002 Location: Shropshire, UK/ Lot, France Posts: 1,848	12 Bolt Diff service Questions I am going to pull the cover on my 12 bolt rear end and change the oil and give it a clean out. I have a new fel-pro gasket to go back on. How much oil does an axle take, I have about 3 litres in the garage, will it need more than this? Should I use sealant with the gasket as well? ny idea on what the bolts should be torqued up to? Which teeth do I count to work out my diff ratio and how do I work it out once I've counted? Any other hints and tips that may help me would be welcomed. Thanks __________________ Phil '67 C10 long fleet. 350/TH350, 4 bbl Carter, K&N, Dual exhaust, loads of stuff coming soon 2001 S10 Blazer Daily Driver, bone stock 4 door 4x4 with manual transmission

07-01-2003, 08:55 AM	#2
ginter Registered User Join Date: Mar 2003 Location: Denver CO. Posts: 156	Not sure exactly how much it takes to fill a GM 12 bolt, but 3 litres (quarts, close enough) will be plenty. You probably already know that you just fill it up to the bottom of the fill hole right? As for the gears, when you get the cover off, count the teeth on the ring gear. It's the biggest gear in there, you can't miss it. It runs the same rotation as the rear wheel and is the cause of the hump in the back of the diff cover. Then count the teeth on the pinion gear. It's the one that is directly connected (more or less) to the drive shaft where it comes into the diff. It's the second biggest gear in there, you can't miss it. Although it's buried in the back there a little bit (front of the differential actually, but you're looking at it from behind the truck so...). A scribe or paint mark near a tooth before you start counting will help here. The gear ratio is just that. The ratio between the ring and pinion. On a 3.07 for example, the pinion gear will turn 3.07 times for every one turn of the ring gear. HTH. __________________ Mike 67 C20 Camper Special - Rust Free! 1970 Porsche 914/6 Last edited by ginter; 07-01-2003 at 08:57 AM.

07-01-2003, 12:53 PM	#4
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,474	Jim you must be right on the oil.My service manual said 4.5 pints.I got a little more than 3.5 before it started to run out the hole. __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

07-01-2003, 09:17 AM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	The differential will take approximately 3 1/2 pints, US measure. I fill and check with my little finger. When I can touch the lube, it is full enough. Usually the ring gear will be stamped with the number of teeth for the ring gear and the pinion, eg: 43:14 which is a 3:07. Jim



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